1. Field of the Invention
The present invention relates generally to apparatus for heating enclosures from the exterior of the enclosure, the apparatus being also suitable for heating outdoor areas by discharging large volumes of heated air toward such areas.
2. Description of the Prior Art
Large capacity heaters are known in the art to be capable of heating fresh air drawn into the heater and passed in non-communicating heat exchanging relation to a flow of heated gaseous combustion products produced by the combustion of an oxidizable material within the heater. Muckelrath, in U.S. Pat. Nos. 3,388,697 and 3,106,200, discloses such heaters, the heaters being typically used to warm relatively large indoor areas from externally thereof, the indoor areas not readily being provided with flues or other venting arrangements which would allow the use of indoor heating apparatus. The heaters discloses in the aforesaid patents also find use in the warming of exterior work areas, such as drilling sites, construction sites, and the like, the relatively warmer work conditions rendered possible by the heaters enabling both men and machinery to perform work under adverse thermal conditions. The heater of U.S. Pat. No. 3,388,697, is comprised of upper and lower tubular members within which non-communicating combustion gas and fresh air passages are defined, the fresh air being pre-heated on intake thereof into the upper tubular member and further heated on passage over exterior surfaces of a fire tube within which an oxidizable material, such as gas or oil, is combusted. The combustion products flow from the lower tubular member to provide heat energy to the pre-heating zone within the upper tubular member prior to venting to ambient from said upper tubular member. Heaters formed of upper and lower tubular members as disclosed in U.S. Pat. No. 3,388,697 do not provide the improved thermal capabilities of the present invention due to a comparatively greater heat loss from such heaters occasioned by the greater exterior surface area presented to ambient by such heaters. The heater of U.S. Pat. No. 3,106,200 provides a similar heater having multiple flow paths, the fresh air and combustion gas flow paths being contained within a single housing. The heater disclosed in this patent does not provide a single fresh air flow path which allows intimate heat exchanging contact between the pre-heated fresh air and the exterior wall surfaces of a fire tube within which an oxidizable material is subjected to combustion. Prior heaters do not provide the thermal advantages provided by the present heating apparatus, the pre-heated fresh air within the present apparatus being brought into full heat exchanging contact with a heated fire tube disposed within lower portions of the housing of the heater. In particular, the present heater provides a fresh air flow circulation which completely surrounds the fire tube and flows along the fire tube for substantially the full length thereof, thereby maximizing heat exchange between the fire tube and the pre-heated fresh air prior to discharge of the heated fresh air into the area to be heated.